What Car? Q&A - Is supermarket diesel inferior?

Q: I know that diesel fuel has to adhere to standards, but do supermarket garages maintain that quality? Does unbranded fuel mean that they reduce the additives to sell the fuel at a lower price? I have heard they do this with petrol, or is this untrue?
Dennis Chester

A: According to the Petrol Retailers' Association, there is no difference between the standard petrol and diesel that you buy from either a franchised fuel station or a supermarket forecourt. In many cases, the fuel is sourced from the same refineries and sometimes delivered in the same tankers.

Supermarkets are prepared to sell their fuel at very little or almost no profit in order to tempt shoppers into the supermarket. The theory is that shoppers will think that if it sells cheap fuel, it'll also sell cheap food.

The difference in fuels is in specialist or premium fuels, such as Shell Optimax and BP Ultimate, which contain additives to improve performance and efficiency. When you buy these fuels, you pay for the special ingredients.